Fabrication, Form, and Function of Morphomechanical Rods

Abstract

From the DNA that encodes our genetics to the giant redwood forests, slender structures are ubiquitous across length scales in nature. Likewise, the canonical rod – objects with two dimensions much smaller than a third – provides the basic unit of engineered structures around us: for example the thread in our clothes and the scaffolds of our homes. However, using deformable rods with controllable shapes and strength to accomplish complex tasks primarily remains the handiwork of biology. For example an octopus arm, elephant trunk, or human arm operates with extreme flexibility, precision, and robustness. The focus of this dissertation is to develop a framework to understand the mechanics and consequently the design for synthetic morphing rods. To develop a cohesive framework, I will focus on three seemingly disparate systems that take lessons from thin-film manufacturing, insect wings, and jewelry making to fabricate rods with controllable shape, size, and stiffness. The first of these systems is bubble casting, which uses a fluid-mediated flow to generate anisotropic balloons that bend when inflated. The second is leveraging core-shell structure inspired by an insect wing to create rods that grow in length when inflated. The third uses packings of spheres – in a tube and on a string – to create granular rods that can stiffen by undergoing a jamming transition. These morphomechanical rods are made using relatively simple methods allowing for their rapid fabrication and alteration. Predictive models of these rods are developed through the iterative exploration of experiment, simulation, and theory. Ultimately, we will examine the critical ingredients that enable programming these rods’ properties and the concomitant mechanics of structures made with these rods. I then show how to use these structures – independently and in unison – to create soft robotics, deployable structures, and functional materials. The accuracy of our modeling results suggest that the framework presented is general to a number of morphing slender structures – thus providing new avenues for the reduced modeling and inverse design of existing systems as well as a launch point for creation of new morphomechanical rod technologies.